| Co-Investigator(Kenkyū-buntansha) |
SONODA Tomoko Chiba University School of Medicine 2nd Dept. Biochemistry, Teaching Assistant, 医学部, 教務職員 (20143307)
ISHIJIMA Sumio Chiba University School of Medicine 2nd Dept. Biochemistry, Instructor, 医学部, 助手 (70184520)
TAIRA Masanori Chiba University School of Medicine 2nd Dept. Biochemistry, Instructor, 医学部, 助手 (60150083)
SUZUKI Nobuo Chiba University School of Medicine 2nd Dept. Biochemistry, Asst. Prof., 医学部, 助教授 (90111426)
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| Research Abstract |
When mammalian cells are stimulated to initiate proliferation or increase protein synthesis, an increase in the synthesis of nucleic acids and nucleotides necessarily follows. Our studies aim at elucidation of the underlying cellular mechanisms by which exogenous stimuli induce increased synthesis of nucleotides, putting emphasis on enzyme regulation of synthesis of phosphoribosyl pyrophosphate(PRPP). PRPP is a primary substrate for the biosynthesis of nucleotides and also a critical activator for the initial enzymes of nucleotide biosynthetic pathways. The results were as follows.
(1) PRPP synthetase was highly purified to a specific activity, the highest in the literature, from rat liver. The protein was composed of several protein species, of which 34 kDa component was identified as the catalytic subsunit. Functions of other components remain to be clarified. (2) Oligonucleotide probes were synthesized based on the partial amino acid sequences of that subunit and were used for screening of a cDNA library from rat Yoshida sarcoma cells. Unexpectedly, two distinct clones were obtained and ensuing studies revealed the presence of at least two highly homologous isoforms of the enzyme subunits(PRS I and II). Furthermore, existence of testis-specific isoform, PRS III, was found and chromosomal localization of the genes for all the isoforms were determined. The structure of rat PRS I gene was elucidated. (3) Various mitogens activated metabolic flux through PRPP into nucleotides as an early response in quiescent mouse fibroblasts (Swiss 3T3) in culture. Neithear protein kinase C nor Ca^<2+> did not appear to be involved in the signal transduction. However, the response completely disappeared in medium devoid of Mg^<2+>. This finding lead to an important proposal that Mg^<2+>, which has not been considered before, does play a critical role in this signal transduction.
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